My brother had a heavy knee injury during his youth. His doctor said he can forget doing sport. Last year he ran a mountainman (full marathon with a descent of 1200m).

He read more into the topic and figured that it is mostly a question of training. Since in my family many do sports, I have seen this many times: have an issue with some joint, back, whatever? Unless you broke a bone or have an open wound that typically means you need to find the right training to get over it.

Usually the worst is not moving at all.